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Ohm's law states that the current passing through a material is directly proportional to the voltage across the device under constant surrounding conditions. German physicist Georg Simon Ohm demonstrated this relationship experimentally in 1827, establishing that electrical current in a metal wire increases proportionally with applied voltage.

Ohmic materials obey Ohm's law, meaning current through them is directly proportional to applied voltage, producing a linear voltage-current relationship. Nonohmic materials do not follow this proportional relationship. Examples of non ohmic devices include diodes and transistors, which exhibit nonlinear current-voltage characteristics.

When voltage and current measurements are plotted on a graph for an ohmic material, the resulting line is linear. The slope of this line directly represents the resistance of the material, calculated as voltage divided by current. This graphical method confirms whether a device behaves as an ohmic conductor.

A voltmeter measures voltage and is connected in parallel with the resistor, while an ammeter measures current and is placed in series with the resistor. Together, these instruments allow researchers to collect paired voltage and current readings across different applied potentials to verify Ohm's law experimentally.

When power supply leads are switched, the current direction reverses. If current initially flows clockwise, reversing the polarity causes it to flow counterclockwise. Both the voltmeter and ammeter readings change sign accordingly, demonstrating that current direction depends on the polarity of the applied voltage.

Ohm's original 1827 experiment measured voltage and current through various simple electrical circuits containing different lengths of wire. His setup consisted of a resistor connected in series with a battery, a voltmeter in parallel with the resistor, and an ammeter in series. Multiple measurements at different voltages revealed the linear relationship now known as Ohm's law.

The linear voltage-current relationship in ohmic materials allows engineers and physicists to predict and control electrical behavior predictably. This proportionality means resistance remains constant across different voltages, making ohmic materials ideal for circuit design and analysis. The consistency of this relationship validates Ohm's law as a fundamental principle in electrical theory.